do they have any historical significance? like fs-40s (first os surpass engine), etc

You probably do mean the first OS 120. They were very good but did have a rather delicate thin casting so not very upstanding a hard crash. I do have a few parts for it like a cylinder head. Do try find a cylinder main casting !

I owned one for a while and flew it in an airplane for a time. I don't remember anything bad about the engine, it just worked OK for me. I do not think there is any historical significance with the engine though.

Don't run them hard. mine had the crankcase come apart and the whole top end of the engine came off. Beat the piston and rod to pieces. Treat them gently and keep the rpm around 8000 and they work quite well.